- Pauson-Khand Reactions with Concomitant C?O Bond Cleavage for the Preparation of 5,5- 5,6- and 5,7-Bicyclic Ring Systems
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Pauson-Khand reactions (PKR) with concomitant C?O bond cleavage have been developed for construction of 5,5- 5,6- and 5,7-bicyclic ring systems bearing complex stereochemistry. The chemistry generates intermolecular PKR-type products in an absolute regio- and stereochemical control which is hardly achievable through real intermolecular Pauson-Khand reactions. A mechanism for this Pauson-Khand reaction has been proposed based on deuterium labelling experiments. (Figure presented.).
- Ma, Ding,Hu, Naifeng,Ao, Junli,Zang, Shaoli,Yu, Guo,Liang, Guangxin
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supporting information
p. 1887 - 1891
(2021/02/26)
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- Chiral Imidazo[1,5- a]pyridine-Oxazolines: A Versatile Family of NHC Ligands for the Highly Enantioselective Hydrosilylation of Ketones
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Herein we report the synthesis and application of a versatile class of N-heterocyclic carbene ligands based on an imidazo[1,5-a]pyridine-3-ylidine backbone that is fused to a chiral oxazoline auxiliary. The key step in the synthesis of these ligands involves the installation of the oxazoline functionality via a microwave-assisted condensation of a cyano-azolium salt with a wide variety of 2-amino alcohols. The resulting chiral bidentate NHC-oxazoline ligands form stable complexes with rhodium(I) that are efficient catalysts for the enantioselective hydrosilylation of structurally diverse ketones. The corresponding secondary alcohols are isolated in good yields (typically >90%) with good to excellent enantioselectivities (80-93% ee). The reported hydrosilylation occurs at ambient temperatures (40 °C), with excellent functional group tolerability. Even ketones bearing heterocyclic substituents (e.g., pyridine or thiophene) or complex organic architectures are hydrosilylated efficiently, which is discussed further in this report.
- Chinna Ayya Swamy,Varenikov, Andrii,Ruiter, Graham De
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supporting information
p. 247 - 257
(2020/02/04)
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- Photocontrolled Cobalt Catalysis for Selective Hydroboration of α,β-Unsaturated Ketones
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Selectivity between 1,2 and 1,4 addition of a nucleophile to an α,β-unsaturated carbonyl compound has classically been modified by the addition of stoichiometric additives to the substrate or reagent to increase their “hard” or “soft” character. Here, we demonstrate a conceptually distinct approach that instead relies on controlling the coordination sphere of a catalyst with visible light. In this way, we bias the reaction down two divergent pathways, giving contrasting products in the catalytic hydroboration of α,β-unsaturated ketones. This includes direct access to previously elusive cyclic enolborates, via 1,4-selective hydroboration, providing a straightforward and stereoselective route to rare syn-aldol products in one-pot. DFT calculations and mechanistic experiments confirm two different mechanisms are operative, underpinning this unusual photocontrolled selectivity switch.
- Beltran, Frédéric,Bergamaschi, Enrico,Funes-Ardoiz, Ignacio,Teskey, Christopher J.
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supporting information
p. 21176 - 21182
(2020/09/17)
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- Chemoselective Luche-Type Reduction of α,β-Unsaturated Ketones by Magnesium Catalysis
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The chemoselective reduction of α,β-unsaturated ketones by use of an economic and readily available Mg catalyst has been developed. Excellent yields for a wide range of ketones have been achieved under mild reaction conditions, short times, and low catalyst loadings (0.2-0.5 mol %).
- Jang, Yoon Kyung,Magre, Marc,Rueping, Magnus
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p. 8349 - 8352
(2019/10/16)
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- Stereodivergent Synthesis of Carveol and Dihydrocarveol through Ketoreductases/Ene-Reductases Catalyzed Asymmetric Reduction
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Chiral carveol and dihydrocarveol are important additives in the flavor industry and building blocks in the synthesis of natural products. Despite the remarkable progress in asymmetric catalysis, convenient access to all possible stereoisomers of carveol and dihydrocarveol remains a challenge. Here, we present the stereodivergent synthesis of carveol and dihydrocarveol through ketoreductases/ene-reductases catalyzed asymmetric reduction. By directly asymmetric reduction of (R)- and (S)-carvone using ketoreductases, which have Prelog or anti-Prelog stereopreference, all four possible stereoisomers of carveol with medium to high diastereomeric excesses (up to >99 %) were first observed. Then four stereoisomers of dihydrocarvone were prepared through ene-reductases catalyzed diastereoselective synthesis. Asymmetric reduction of obtained dihydrocarvone isomers by ketoreductases further provide access to all eight stereoisomeric dihydrocarveol with up to 95 % de values. In addition, the absolute configurations of dihydrocarveol stereoisomers were determined by using modified Mosher's method.
- Guo, Jiyang,Zhang, Rui,Ouyang, Jingping,Zhang, Feiting,Qin, Fengyu,Liu, Guigao,Zhang, Wenhe,Li, Hengyu,Ji, Xiaohong,Jia, Xian,Qin, Bin,You, Song
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p. 5496 - 5504
(2018/11/30)
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- Photoinduced Carboborative Ring Contraction Enables Regio- and Stereoselective Synthesis of Multiply Substituted Five-Membered Carbocycles and Heterocycles
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We report herein a photoinduced carboborative ring contraction of monounsaturated six-membered carbocycles and heterocycles. The reaction produces substituted five-membered ring systems stereoselectively and on preparative scales. The products feature multiple stereocenters, including contiguous quaternary carbons. We show that the reaction can serve as a synthetic platform for ring system alteration of natural products. The reaction can also be used in natural product synthesis. A concise total synthesis of artalbic acid has been enabled by a sequence of photoinduced carboborative ring contraction, Rauhut-Currier reaction, and nitrilase-catalyzed hydrolysis. The synthetic utility of the reaction has been further demonstrated by converting the intermediate organoboranes to alcohols, amines, and alkenes.
- Jin, Shengfei,Nguyen, Vu T.,Dang, Hang T.,Nguyen, Dat P.,Arman, Hadi D.,Larionov, Oleg V.
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supporting information
p. 11365 - 11368
(2017/08/30)
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- Hydrogenation of Carbonyl Derivatives with a Well-Defined Rhenium Precatalyst
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The first efficient and general rhenium-catalyzed hydrogenation of carbonyl derivatives was developed. The key to the success of the reaction was the use of a well-defined rhenium complex bearing a tridentate diphosphinoamino ligand as the catalyst (0.5 mol %) at 70 °C in the presence of H2 (30 bar). The mechanism of the reaction was investigated by DFT(PBE0-D3) calculations.
- Wei, Duo,Roisnel, Thierry,Darcel, Christophe,Clot, Eric,Sortais, Jean-Baptiste
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- Synthesis and properties of novel chiral imidazolium-based ionic liquids derived from carvone
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A large series of novel chiral imidazolium ionic liquids were synthesized using the terpenoid carvone as the chiral substrate. Their specific rotations were characterized and their potential use in chiral recognition was demonstrated by studying interactions with racemic Mosher's acid salt.
- Santamarta, Francisco,Vilas, Miguel,Tojo, Emilia,Fall, Yagamare
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p. 31177 - 31180
(2016/04/08)
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- A General CuCl2-Promoted Alkene Aminochlorination Reaction
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A CuCl2-promoted alkene aminochlorination reaction has been developed. A variety of anilides that contain a mono-, di-, or trisubstituted alkenyl moiety readily participated in this reaction to afford structurally diverse vicinal chloroamines. Studies suggest that the process proceeds by a radical-type mechanism and that CuCl2serves as both the oxidant to generate the amidyl radical as well as the chloride source.
- Li, Shu-Qi,Xiong, Peng,Zhu, Lin,Qian, Xiang-Yang,Xu, Hai-Chao
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supporting information
p. 3449 - 3455
(2016/07/23)
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- TERPENE AND TERPENOID DERIVATIVES CONTAINING VINYL GROUPS FOR THE PREPARATION OF POLYMERS
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The invention relates to a method for producing functionalised monomers, the method comprising: a) providing a starting material selected from terpenes and terpenoids; b) forming a derivative of the starting material by incorporation of a hydroxyl group; c) esterifying the hydroxyl group of the derivative to introduce a moiety containing a vinyl group, so as to produce a functionalised monomer. The functionalised monomer can be polymerised to obtain a bio-derived polymer.
- -
-
Page/Page column 46; 49
(2015/11/10)
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- Comparative anticonvulsant study of epoxycarvone stereoisomers
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Stereoisomers of the monoterpene epoxycarvone (EC), namely (+)-cis-EC, (-)-cis-EC, (+)-Trans-EC, and (-)-Trans-EC, were comparatively evaluated for anticonvulsant activity in specific methodologies. In the pentylenetetrazole (PTZ)-induced anticonvulsant test, all of the stereoisomers (at 300 mg/kg) increased the latency to seizure onset, and afforded 100% protection against the death of the animals. In the maximal electroshock-induced seizures (MES) test, prevention of tonic seizures was also verified for all of the isomers tested. However, the isomeric forms (+) and (-)-Trans-EC showed 25% and 12.5% inhibition of convulsions, respectively. In the pilocarpine-induced seizures test, all stereoisomers demonstrated an anticonvulsant profile, yet the stereoisomers (+) and (-)-Trans-EC (at 300 mg/kg) showed a more pronounced effect. A strychnine-induced anticonvulsant test was performed, and none of the stereoisomers significantly increased the latency to onset of convulsions; the stereoisomers probably do not act in this pathway. However, the stereoisomers (+)-cis-EC and (+)-Trans-EC greatly increased the latency to death of the animals, thus presenting some protection. The four EC stereoisomers show promise for anticonvulsant activity, an effect emphasized in the isomers (+)-cis-EC, (+)-Trans-EC, and (-)-Trans-EC for certain parameters of the tested methodologies. These results serve as support for further research and development of antiepileptic drugs from monoterpenes.
- Salgado, Paula Regina Rodrigues,Da Fonsêca, Diogo Vilar,Braga, Renan Marinho,De Melo, Cynthia Germoglio Farias,Andrade, Luciana Nalone,De Almeida, Reinaldo Nóbrega,De Sousa, Dami?o Pergentino
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p. 19660 - 19673
(2015/12/23)
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- Eco-friendly stereoselective reduction of α,β-unsaturated carbonyl compounds by Er(OTf)3/NaBH4 in 2-MeTHF
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An operationally simple and environmentally benign catalytic procedure has been developed to selectively reduce different α,β-unsaturated ketones. The corresponding allylic alcohols are obtained with high chemo- and diastereoselectivity using Er(OTf)3 and NaBH4 in 2-MeTHF. This protocol reduces the amount of catalyst and NaBH4 needed, compared to classical procedures and the stages of extraction/purification are carried out in aqueous solutions avoiding the use of toxic solvents. Taking into account that Er(OTf)3 can be considered even less toxic than table salt and the 'greenness' of 2-MeTHF as a solvent, the system Er(OTf)3/2-MeTHF can be proposed as a cheap, efficient, and environmentally sustainable reduction system for the synthesis of allylic alcohols.
- Nardi, Monica,Sindona, Giovanni,Costanzo, Paola,Oliverio, Manuela,Procopio, Antonio
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p. 1132 - 1135
(2015/02/19)
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- Borinic Acid Catalyzed, Regioselective Chloroacylations and Chlorosulfonylations of 2,3-Epoxy Alcohols
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In the presence of a borinic acid derived catalyst, 2,3-epoxy alcohols undergo couplings with acyl and sulfonyl chlorides. This transformation directly generates O-acylated or O-sulfonylated chlorohydrin diols, with significant levels of regioselectivity for both the ring-opening and O-functionalization steps.
- Tanveer, Kashif,Jarrah, Kareem,Taylor, Mark S.
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supporting information
p. 3482 - 3485
(2015/07/28)
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- Engineering Rieske Non-Heme Iron Oxygenases for the Asymmetric Dihydroxylation of Alkenes
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The asymmetric dihydroxylation of olefins is of special interest due to the facile transformation of the chiral diol products into valuable derivatives. Rieske non-heme iron oxygenases (ROs) represent promising biocatalysts for this reaction as they can be engineered to efficiently catalyze the selective mono- and dihydroxylation of various olefins. The introduction of a single point mutation improved selectivities (≥95 %) and conversions (>99 %) towards selected alkenes. By modifying the size of one active site amino acid side chain, we were able to modulate the regio- and stereoselectivity of these enzymes. For distinct substrates, mutants displayed altered regioselectivities or even favored opposite enantiomers compared to the wild-type ROs, offering a sustainable approach for the oxyfunctionalization of a wide variety of structurally different olefins. Modulation by mutation: Rieske non-heme iron oxygenases can be used as efficient biocatalysts for the selective oxyfunctionalization of various olefins yielding vicinal cis-diols and allylic alcohols. Introduction of a single amino acid substitution in the active sites of two selected oxygenases resulted in variants with improved stereoselectivities and product formations.
- Gally, Christine,Nestl, Bettina M.,Hauer, Bernhard
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supporting information
p. 12952 - 12956
(2015/11/02)
-
- Substrate flexibility and reaction specificity of tropinone reductase-like short-chain dehydrogenases
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Annotations of protein or gene sequences from large scale sequencing projects are based on protein size, characteristic binding motifs, and conserved catalytic amino acids, but biochemical functions are often uncertain. In the large family of short-chain dehydrogenases/reductases (SDRs), functional predictions often fail. Putative tropinone reductases, named tropinone reductase-like (TRL), are SDRs annotated in many genomes of organisms that do not contain tropane alkaloids. SDRs in vitro often accept several substrates complicating functional assignments. Cochlearia officinalis, a Brassicaceae, contains tropane alkaloids, in contrast to the closely related Arabidopsis thaliana. TRLs from Arabidopsis and the tropinone reductase isolated from Cochlearia (CoTR) were investigated for their catalytic capacity. In contrast to CoTR, none of the Arabidopsis TRLs reduced tropinone in vitro. NAD(H) and NADP(H) preferences were relaxed in two TRLs, and protein homology models revealed flexibility of amino acid residues in the active site allowing binding of both cofactors. TRLs reduced various carbonyl compounds, among them terpene ketones. The reduction was stereospecific for most of TRLs investigated, and the corresponding terpene alcohol oxidation was stereoselective. Carbonyl compounds that were identified to serve as substrates were applied for modeling pharmacophores of each TRL. A database of commercially available compounds was screened using the pharmacophores. Compounds identified as potential substrates were confirmed by turnover in vitro. Thus pharmacophores may contribute to better predictability of biochemical functions of SDR enzymes.
- Reinhardt, Nicole,Fischer, Juliane,Coppi, Ralph,Blum, Elke,Brandt, Wolfgang,Draeger, Birgit
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-
- Titanocene-promoted stereoselective eliminations on epoxy alcohols derived from R-(-)-carvone
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The reaction of several stereoisomeric epoxy alcohols, obtained from R-(-)-carvone, and their corresponding formates, acetates, and benzoates, promoted by Cp2TiCl has been studied. The different outcomes of the reaction of epoxy derivatives are rationalized in terms of mechanistically biased processes. The radicals emerging from oxirane cleavage provide two types of reaction: dehydroxylation (deoxycarbonylation) and dehydrogenation. The results offer considerable support for the radical elimination theory of hydroxyl, formyloxyl, and acetoxyl groups. The inability of tertiary radicals to be reduced by the Ti(III) complex is demonstrated unequivocally.
- Fernández-Mateos,Herrero Teijón,Rubio González
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p. 1611 - 1616
(2013/02/25)
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- Total synthesis of cyrneine A
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Neuritogenic natural products: The tricyclic diterpene cyrneineA featuring a hexatrienal unit was prepared synthetically for the first time by a Heck reaction, a carbene ring expansion, and a reductive carbonylation. The structure of the natural product was assigned by X-ray crystal analysis of a synthetic sample. Copyright
- Elamparuthi, Elangovan,Fellay, Cindy,Neuburger, Markus,Gademann, Karl
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supporting information; experimental part
p. 4071 - 4073
(2012/06/01)
-
- Influence of the Br?nsted and Lewis acid sites on the catalytic activity and selectivity of Fe/MCM-41 system
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The system Fe2O3/MCM-41, with high iron dispersion, was synthesized in order to introduce Lewis acid sites into the MCM-41 structure. Two calcination atmospheres (inert and oxidant) were used to produce iron nanoclusters with different structural properties. Besides, a silylation treatment was realized on both solids with the aim of neutralizing the Br?nsted acidity associated with the MCM-41 silanol groups. The samples were characterized by atomic absorption spectroscopy, X-ray diffraction at low angles, N2 adsorption, temperature-programmed reduction, Fourier transform infrared spectroscopy, nuclear magnetic resonance of 29Si, and M?ssbauer spectroscopy. The influence of the structural changes of the nanoclusters and the effect of the simultaneous presence of Lewis and Br?nsted acid sites were evaluated studying the product distribution from the α-pinene oxide isomerization reaction. It was determined that the Br?nsted acidity of the Fe/MCM-41 system has not the sufficient acid strength to modify the product distribution which is mainly governed by the Lewis sites.
- Fellenz,Bengoa,Marchetti,Gervasini
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scheme or table
p. 187 - 196
(2012/10/08)
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- Air-stable, nitrile-ligated (cyclopentadienone)iron dicarbonyl compounds as transfer reduction and oxidation catalysts
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A series of air-stable, nitrile-ligated (cyclopentadienone)iron dicarbonyl compounds was synthesized and their activities as catalysts in the transfer reduction of acetophenone were explored. While all were active catalysts, the acetonitrile adduct was chosen for further study and was found to be active in the transfer reduction of aldehydes and ketones and in the Oppenauer-type oxidation of secondary alcohols. The acetonitrile catalyst exhibited activities similar to those of an analogous air-sensitive iron hydride, but unlike the iron hydride it was unreactive in carbonyl reductions using hydrogen gas. Copyright
- Plank, Taylor N.,Drake, Jessica L.,Kim, Daniel K.,Funk, Timothy W.
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supporting information; experimental part
p. 597 - 601
(2012/05/04)
-
- Enantioselective synthesis of a key A-ring intermediate for the preparation of 1α,25-dihydroxyvitamin D3
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A novel approach to the key A-ring α, β-unsaturated aldehyde 1, an important intermediate for the preparation of 1α,25-dihydroxyvitamin D3, has been developed. The strategy started from the inexpensive starting material (R)-carvone with an ene reaction serving as the key step toward the potential synthesis of vitamin D3 analogues bearing the modification at the C-2 position.
- Chen, Yan,Ju, Tong
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supporting information; experimental part
p. 86 - 89
(2011/04/12)
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- Dauben-Michno oxidative transposition of allylic cyanohydrins - Enantiomeric switch of (-)-carvone to (+)-carvone
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Allylic cyanohydrins were subjected to Dauben-Michno oxidation at low temperatures to provide β-cyanoenones in good to excellent yields. The potential of this oxidative transposition as a means of an enantiomeric switch of enones containing a latent plane of symmetry was tested by conversion of (-)-carvone to its enantiomer.
- Hudlicky, Jason R.,Werner, Lukas,Semak, Vladislav,Simionescu, Razvan,Hudlicky, Tomas
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scheme or table
p. 535 - 543
(2011/10/03)
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- Chiral building blocks from R-(-)-carvone: N-bromosuccinimidemediated addition-sceletal rearrangement of (-)-cis-carveol
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Synthetically valuable bicyclic blocks 5, 7 and 9 were prepared by the oxidative cleavage of the double bond of 4 with the RuCl3-NaIO4 system and O3.
- Valeev, Ruslan F.,Selezneva, Nataliya K.,Starikova, Zoya A.,Pankrat'ev, Evgenii Yu.,Miftakhov, Mansur S.
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scheme or table
p. 77 - 79
(2010/06/19)
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- New orthogonally functionalized synthetic blocks from R-(-)-carvone
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The intramolecular cyclization of (-)-cis-carveol under iodine treatment afforded (1R,5R,6S)-6-iodomethyl-2,6-dimethyl-7-oxabicyclo[3.2.1]oct-2-ene that was subjected to allyl oxydation with the complex CrO3DMP giving a synthetically valuable building block, (1R,5R,6S)-6-iodomethyl-2,6-dimethyl-7- oxabicyclo[3.2.1]oct-2-ene-4-one. In the latter the double bond was cleaved by ozonization to obtain the expected trioxo derivative, and the subsequent ozonolysis of its enol form provided a multiple functionalized tetrahydrofuran derivative. Pleiades Publishing, Ltd., 2010.
- Valeev,Khasanova,Miftakhov
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experimental part
p. 670 - 673
(2010/10/04)
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- Synthesis and some transformations of (-)-carveol
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Reduction of the oxo group in (-)-carvone with LiAlH4, NaBH4, and (i-Bu)2AlH was performed. It was found that the reduction with the system CeCl3 ? 7 H2O-NaBH4 in methanol at 20°C is the most practical procedure for the synthesis of (-)-carveol. Solvolysis of (-)-carvyl methanesulfonate gave products of SN2 and SN2' replacement of the methylsulfonyloxy group, the latter slightly prevailing. Overman rearrangement of (-)-carveol resulted in the formation of the corresponding trichloroacetamide derivative, and intramolecular iodoetherification of the title compound afforded 6-iodomethyl-2,6-dimethyl-7-oxabicyclo[3.2.1]oct-2-ene. Pleiades Publishing, Ltd., 2009.
- Valeev,Vostrikov,Miftakhov
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experimental part
p. 810 - 814
(2009/12/09)
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- Metal-catalyzed silylene insertions of allylic ethers: Stereoselective formation of chiral allylic silanes
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Silylene insertion into allylic ethers occurs suprafacially to provide enantioenriched allylic silanes and disilanes. Silylene insertion to a variety of protected allylic alcohols utilizing silver- and copper-mediated conditions proved to be a general method for allylic silane formation. Allylic disilanes reacted similarly to allylic silanes, undergoing both annulation and allylation reactions. Copyright
- Bourque, Laura E.,Cleary, Pamela A.,Woerpel
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p. 12602 - 12603
(2008/09/16)
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- Pyridinium chlorochromate mediated oxidative cyclisation of sterically crowded γ,δ-unsaturated alcohols
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Pyridinium chlorochromate (PCC) mediated oxidative cyclisation of sterically crowded γ,δ-unsaturated alcohols (primary, secondary, allylic, benzylic as well as tertiary) is described.
- Srikrishna,Vasantha Lakshmi,Sudhakar
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p. 7610 - 7613
(2008/03/14)
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- Synthesis of enantiomerically pure β-azidoselenides starting from natural terpenes
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Several unsaturated natural terpenes have been easily converted, in good yields, into the corresponding enantiomerically pure β-azidoselenides by addition of the electrophilic selenium reagent PhSeOTf in the presence of sodium azide. These reactions are stereospecific anti additions, which occur with a Markovnikov orientation. Examples of the synthetic importance of these β-azidoselenides are also reported.
- Tiecco, Marcello,Testaferri, Lorenzo,Santi, Claudio,Tomassini, Cristina,Santoro, Stefano,Marini, Francesca,Bagnoli, Luana,Temperini, Andrea
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p. 12373 - 12378
(2008/03/14)
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- Cyclic allyl carbamates in stereoselective syn SE′ processes: Synthetic approach to sarcodictyins and eleutherobin
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Our synthetic approach of marine diterpenoids sarcodictyins A and B and eleutherobin relies on the one-step attachment of a C5-C9 side chain at the C10 position. The C1, C10 cis-disubstituted cyclohexene derivative is obtained in 86 % yield with total stereoselectivity. The reaction is based on a syn S E′ process involving a cyclic (Z)-allyl diisopropylcarbamate. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Dhulut, Sylvie,Bourin, Arnaud,Lannou, Marie-Isabelle,Fleury, Etienne,Lensen, Nathalie,Chelain, Evelyne,Pancrazi, Ange,Ardisson, Janick,Fahy, Jacques
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p. 5235 - 5243
(2008/03/18)
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- A radical cyclisation based cyclopentenone annulation of allyl alcohols
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A four-step cyclopentenone annulation reaction of allylic alcohols employing a 5-exo-trig radical cyclisation reaction of mixed allyl methyl ketals of bromoacetone as the key step is described. The annulated product 12b obtained from 2,3-dimethylcyclohexenol has been further elaborated into (±)-epibakkenolides employing a 5-exo-dig radical cylisation reaction based α-spiro-β-methylene-γ-butyrolactone annulation methodology.
- Srikrishna,Viswajanani,Sattigeri
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p. 2975 - 2983
(2007/10/03)
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- Stereoselective synthesis of enantiomerically pure, orthogonally protected 2-methylenecyclohexane-1,3,5-triols and 2,4,6-trihydroxycyclohexanones
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The triply silyl protected 2-methylenecyclohexane-1,3,5-triols 1a-c (C-1: tert-butyldimethylsilyl, TBDMS; C-3: trimethylsilyl, TMS; C-5: tert-butyldiphenylsilyl, TBDPS) were prepared from (R)-(-)-carvone in seven synthetic steps (overall yields: 29-53%). Ozonolysis in the presence of triethylamine yielded the triply protected 2,4,6-trihydroxycyclohexanones 2a-c (85%-quant.). The configuration of the products was proven by NOESY studies and by chemical correlation.
- Kirsch, Stefan,Bach, Thorsten
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p. 1827 - 1836
(2007/10/03)
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- First comprehensive bakkane approach: Stereoselective and efficient dichloroketene-based total syntheses of (±)- and (-)-9-acetoxyfukinanolide, (±)- and (+)-bakkenolide a, (-)-bakkenolides III, B, C, H, L, V, and X, (±)- and (-)-homogynolide A, (±)-homogynolide B, and (±)-palmosalide C
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Cycloaddition of dichloroketene with dimethylcyclohexenes has been used as the key reaction in an efficient, general approach to the bakkanes. New methods and methodologies that have been developed in this work include spiro β-methylene-γ-butyrolactonizations, a vicinal dicarboxylation, an angelic ester preparation, a transesterification, an epoxy ketone double reduction, and a retro aldol-aldol approach to low-energy aldol isomers.
- Brocksom, Timothy J.,Coelho, Fernando,Depres, Jean-Pierre,Greene, Andrew E.,Freire de Lima, Marco E.,Hamelin, Olivier,Hartmann, Benoit,Kanazawa, Alice M.,Wang, Yanyun
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p. 15313 - 15325
(2007/10/03)
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- Modelling the biokinetic resolution of diastereomers present in unequal initial amounts
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The enantiomeric ratio (E) is commonly used to evaluate enzyme-catalysed kinetic resolutions. Chen et al. (1982) proposed a model for the enantiomeric ratio, which relates the extent of substrate conversion and the enantiomeric excess. The model, however,
- De Carvalho, Carla C.C.R.,Van Keulen, Frederik,Da Fonseca, M.Manuela R.
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p. 1637 - 1643
(2007/10/03)
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- Sex differences in the metabolism of (+)- and (-)-limonene enantiomers to carveol and perillyl alcohol derivatives by cytochrome P450 enzymes in rat liver microsomes
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(+)-Limonene is reported to cause nephropathy in male rats, but not in female rats and other species of animals including mice, rabbits, guinea pigs, and dogs. Male rats contain high levels of α2u-globulin in kidneys, and it has been shown that limonene a
- Miyazawa, Mitsuo,Shindo, Masaki,Shimada, Tsutomu
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- Chemoselective Hydrogen Transfer Reduction of Unsaturated Ketones to Allylic Alcohols with Solid Zr and Hf Catalysts
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α,β-Unsaturated ketones were reduced to allylic alcohols with high chemo- and diastereoselectivity, using Zr and Hf compounds heterogenised on mesoporous molecular sieves.
- De Bruyn, Mario,De Vos, Dirk E.,Jacobs, Pierre A.
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p. 1120 - 1125
(2007/10/03)
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- Chiral synthons from carvone. Part 50. Enantiospecific approaches to both enantiomers of bicyclo[4.3.0]nonane-3,8-dione derivatives
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Enantiospecific synthesis of both enantiomeric forms of bicyclo[4.3.0]nonane-3,8-dione derivatives has been described starting from (R)-carvone employing two different cyclopentannulation methodologies. Thus, in the first methodology, carveol (5) was converted into tricyclic ketone 4 employing a Claisen rearrangement and intramolecular diazo ketone cyclopropanation reactions. Degradation of the isopropenyl group followed by cyclopropane cleavage and cuprate addition generated the dione (-)-12a. Whereas, a Wacker mediated cyclopentannulation of (R)-carvone via the dione 15 furnished the, enone 17. Functional group manipulation including the degradation of isopropenyl group transformed the enone 17 into the dione (+)-12a, which on regioselective ketalisation generated the ketoketal (+)-2.
- Srikrishna,Reddy, T. Jagadeeswar
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p. 2040 - 2046
(2007/10/03)
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- Percutaneous absorption of the montoterperne carvone: implication of stereoselective metabolism on blood levels.
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The purpose of this study was to determine whether an enantioselective difference in the metabolism of topically applied R-(-)- and S-(+)-carvone could be observed in man. In a previous investigation we found that R-(-)- and S-(+)-carvone are stereoselectively biotransformed by human liver microsomes to 4R,6S-(-)- and 45,6S-(+)-carveol, respectively, and 4R,6S-(-)-carveol is further glucuronidated. We therefore investigated the metabolism and pharmacokinetics of R-(-)- and S-(+)-carvone in four healthy subjects using chiral gas chromatography as the analytical method. Following separate topical applications at a dose of 300 mg, R-(-)- and S-(+)-carvone were rapidly absorbed, resulting in significantly higher Cmax levels for S-(+)-carvone (88.0 vs 23.9 ng mL(-1)) and longer distribution half-lives (t(1/2alpha)) (19.4 vs 7.8 min), resulting in 3.4-fold higher areas under the blood concentration-time curves (5420 vs 1611 ng min mL(-1)). The biotransformation products for both enantiomers in plasma were below detection limit. Analysis of control- and beta-glucuronidase pretreated urine samples, however, revealed a stereoselective metabolism of R-(-)-carvone to 4R,6S-(-)-carveol and 4R,6S-(-)-carveol glucuronide. No metabolites could be found in urine samples after S-(+)-carvone application. These data indicate that stereoselectivity in phase-I and phase-II metabolism has significant effects on R-(-)- and S-(+)-carvone pharmacokinetics. This might serve to explain the increased blood levels of S-(+)-carvone.
- Jaeger,Mayer,Reznicek,Buchbauer
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p. 637 - 642
(2007/10/03)
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- A simple and efficient protocol for epoxidation of olefins using dimethyldioxirane
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The reaction of a series of monoterpenic olefins and Δ4-octalins with dimethyldioxirane led to the corresponding epoxides in excellent yields. Remarkable diastereoselectivity was observed for the Δ4-octalins. The procedure consists simply in stirring the substrate, NaHCO3 and acetone, at 0°C, with dropwise addition of an aqueous solution of oxone. (C) 2000 Elsevier Science Ltd.
- Ferraz, Helena M. C.,Muzzi, Rozanna M.,De O. Vieira, Tiago,Viertler, Hans
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p. 5021 - 5023
(2007/10/03)
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- Stereoselective metabolism of the monoterpene carvone by rat and human liver microsomes
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The large amounts of carvone enantiomers consumed as food additives and in dental formulations justifies the evaluation of their biotransformation pathway. The in-vitro metabolism of R-(-)- and S-(+)-carvone was studied in rat and human liver microsomes using chiral gas chromatography. Stereoselective biotransformation was observed when each enantiomer was incubated separately with liver microsomes. 4R, 6S-(-)-Carveol was NADPH-dependently formed from R-(-)-carvone, whereas 4S, 6S-(+)-carveol was produced from S-(+)-carvone. Metabolite formation followed Michaelis-Menten kinetics exhibiting a significant lower apparent K(m) (Michaelis-Menten Constant) for 4R, 6S-(-)-carveol compared with 4S, 6S-(+)-carveol in rat and human liver microsomes (28.4±10.6 μM and 69.4±10.3 μM vs 33.6±8.5 μM and 98.3±22.4 μM). The maximal formation rate (V(max)) determined in the same microsomal preparations yielded 30.2±5.0 and 32.3±3.9 pmol (mg protein)-1 min-1 in rat liver and 55.3±5.7 and 65.2±4.3 pmol (mg protein)-1 min-1 in human liver microsomes. Phase II conjugation of the carveol isomers by rat and human liver microsomes in the presence of UDPGA (uridine S'-diphosphogluaronic acid) only revealed glucuronidation of 4R, 6S-(-)-carveol. V(max) for glucuronide formation was more than 4-fold higher in the rat liver compared with human liver preparations (185.9±34.5 and 42.6±7.1 pmol (mg protein)-1 min-1, respectively). K(m) values, however, showed no species-related difference (13.9±4.1 μM and 10.2±2.2 μM). This study demonstrated stereoselectivity in phase-I and phase-II metabolism for R-(-)- and S-(+)-carvone and might be predictive for carvone biotransformation in man.
- Jaeger, Walter,Mayer, Marion,Platzer, Peter,Reznicek, Gottfried,Dietrich, Hermann,Buchbauer, Gerhard
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p. 191 - 197
(2007/10/03)
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- A 38 kDa allylic alcohol dehydrogenase from the cultured cells of Nicotiana tabacum
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An NADP+-dependent alcohol dehydrogenase (allyl-ADH) was isolated from the cultured cells of Nicotiana tabacum. The allyl-ADH was found to be efficient for the dehydrogenation of secondary allylic alcohols rather than saturated secondary alcohols and it was specific for the S-stereoisomer of the alcohols. The enzyme catalyzed the reversible reaction whereby the carbonyl group of enones is reduced to the corresponding allylic alcohol or vice versa. Two possible primary structures of the allyl-ADH were deduced by the sequence analyses of full-length cDNAs (ally-ADH1 and ally-ADH2), which were cloned by the PCR method. These analyses indicated that the allyl-ADHs are composed of 343 amino acids-having the molecular weights 38 083 and 37 994, respectively, and they showed approximately 70% homology to the NADP+-dependent oxidoreductases belonging to a plant ζ-crystallin family. (C) 2000 Elsevier Science Ltd.
- Hirata, Toshifumi,Tamura, Yoshitaka,Yokobatake, Naoyuki,Shimoda, Kei,Ashida, Yoshiyuki
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p. 297 - 303
(2007/10/03)
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- Synthesis of chiral bicyclo[4.3.1]decanes via an intramolecular carbonyl ene-reaction
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Synthesis of chiral bicyclo[4.3.1]decanes via an intramolecular acid catalysed type II ene reaction of chiral (5-isopropenylcyclohex-2- enyl)acetaldehydes derived from (R)-carvone is described.
- Srikrishna,Dinesh,Anebouselvy
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p. 1031 - 1034
(2007/10/03)
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- Synthesis of novel antifungal agents (2)
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Synthesis of novel cyclohexyl analogs of restricticin using intramolecular radical cyclization and their in vitro and in vivo antifungal activities are described.
- Tsukuda, Takuo,Watanabe, Masami,Ontsuka, Hitomi,Hattori, Kazuo,Shirai, Michio,Shimma, Nobuo
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p. 1825 - 1828
(2007/10/03)
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- Asymmetric hydrogenation of cyclic α,β-unsaturated ketones to chiral allylic alcohols
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The Ru(II)-BINAP-1,2-diphenylethylenediamine combined catalyst system effects asymmetric hydrogenation of certain cyclic enones in 2-propanol containing KOH with a substrate/catalyst molar ratio of 250 to 2500. The hydrogenation occurs selectively at the C=O function with excellent enantio- or diastereoselectivity.
- Ohkuma, Takeshi,Ikehira, Hideyuki,Ikariya, Takao,Noyori, Ryoji
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p. 467 - 468
(2007/10/03)
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- Opening of cyclopropyl ketones with SmI2 . Synthesis of spirocyclic and bicyclic ketones by intramolecular trapping of an electrophile
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A method for the opening of cyclopropyl ketones with samarium (II) iodide followed by the intramolecular trapping of an electrophile is described. This process leads to the obtainment of functionalized spirocyclic, bicyclic, and tricyclic ketones in moderate to good yields.
- Molander, Gary A.,Alonso-Alija, Cristina
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p. 8067 - 8084
(2007/10/03)
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- Enantioselective synthesis of both (+)-and (-)-derivatives of bicyclo[4.3.0]nonan-8-one and -3,8-diones from R-carvone 1
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Enantioselective synthesis of both the enantiomeric forms of the hydrindane derivatives mentioned in the title, potential chiral precursors in terpenoid synthesis, starting from R-carvone employing two different cyclopentannulation methodologies is described.
- Srikrishna, Adusumilli,Reddy, T. Jagadeeswar,Nagaraju, Sankuratri
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p. 1679 - 1682
(2007/10/03)
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- Highly regio- and stereoselective reductions of carbonyl compounds in aqueous glycosidic media
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Highly regioselective reductions of α,β-unsaturated ketones to the corresponding allylic alcohols were performed in essentially quantitative yields in aqueous media containing either glycosidic surfactants or amphiphilic carbohydrates. Reductions of cyclohexanones and cyclohexenones lead under the same conditions, stereoselectively to reduced compounds bearing an equatorial alcohol function. Hydrophobic interactions between amphiphilic carbohydrates and lipophilic substrates were modelized and should account for the observed stereodifferentiation.
- Denis, Cecile,Laignel, Benoit,Plusquellec, Daniel,Le Marouille, Jean-Yves,Botrel, Alain
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- Synthetic Chemistry with Fullerenes. Photooxygenation of Olefins
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Under irradiation with visible or UV (>290 nm) light in the presence of molecular oxygen and a minute amount of fullerenes, olefins and dienes undergo ene and Diels-Alder reactions with singlet oxygen to give photooxygenation products.The regio- and stereoselectivities of the photooxygenation of β-myrcene, (+)-pulegone, 4-methylpent-3-en-2-ol, and (+)-limonene were very similar to those observed in known singlet oxygen reactions, indicating that the fullerene-sensitized reaction generates free singlet oxygen.The efficiency of fullerenes and conventional sensitizers was qualitatively examined by using the Diels-Alder reaction between 1O2 and furan-2-carboxylic acid as a probe.Among those examined, C70 was found to be the most effective.The reaction was the fastest and completed with as little as 0.0001 equiv of C70.C60 and hematoporphyrin were found to be of similar efficiency.The methanofullerene 13, which lacks one olefinic conjugation in the C60 core, was as good as C60 itself, but the aminofullerene 14, lacking six double bonds, was quite inferior.The fullerene carboxylic acid 15, which was previously shown to show considerable biochemical activity, was found to be capable of generating singlet oxygen in aqueous DMSO.
- Tokuyama, Hidetoshi,Nakamura, Eiichi
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p. 1135 - 1138
(2007/10/02)
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- Aminoborohydrides. 4. The Synthesis and Characterization of Lithium Aminoborohydrides: A New Class of Powerful, Selective, Air-Stable Reducing Agents
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Lithium aminoborohydrides (LiABH3) are a new class of powerful yet selective reducing agents that reproduce, in air, virtually all of the transformations for which lithium aluminum hydrides is now used.LiABH3's can be readily prepared as solids or generated in situ, are nonpyrophoric, and liberate hydrogen only slowly with protic solvents above pH 4.LiABH3's can be handled in dry air as easily as sodium borohydride and retain their chemical activity for at least 6 month when stored under nitrogen or dry air at 25 deg C.LiABH3's can be synthesized from any primary or secondary amine, thus allowing control of the steric and electronic environment of these reagents.
- Fisher, Gary B.,Fuller, Joseph C.,Harrison, John,Alvarez, Salvador G.,Burkhardt, Elizabeth R.,et al.
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p. 6378 - 6385
(2007/10/02)
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- Formal total synthesis of (-)-dendrobine using zirconium-promoted reductive cyclization
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The alkaloid (-)-dendrobine was synthesized from (+)-calvone by a short sequence using zirconium-promoted reductive cyclization. The absolute configuration of a synthetic intermediate was determined by an improved version of Mosher's method.
- Uesaka,Saitoh,Mori,Shibasaki,Okamura,Date
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p. 5633 - 5642
(2007/10/02)
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- Photosensitized Oxygenation of Olefins with Zinc Tetraphenylporphine-1,4-Diazabicyclooctane Complex
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In the presence of a proper amount of amines such as 1,4-diazabicyclooctane (DABCO) and piperidine, zinc tetraphenylporphine (ZnTPP) works as a not only apparently more effective but also more photoresistant sensitizer for singlet-oxygen oxygenation of olefins than in the absence of the amines.This is ascribed to the facts that ZnTPP forms a 1:1 complex with DABCO, and that DABCO coordinated to ZnTPP has no ability to quench singlet oxygen, as revealed by detection of singlet oxygen phosphorescence and product distributions in oxygenation of d-limonene, 1,2-dimethylcyclohexene, and 1-phenylcyclobutene.
- Sakuragi, Masako,Ichimura, Kunihiro,Sakuragi, Hirochika
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p. 1944 - 1949
(2007/10/02)
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- Cleavage of 2,3-Epoxyalkylhalides by the Sonochemical Zinc-Copper Couple
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2,3-Epoxyalkylhalides are readily transformed into allylic alcohols when sonicated in the presence of a zinc-copper couple in aqueous ethanol.
- Sarandeses, Luis A.,Mourino, Antonio,Luche, Jean-Louis
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p. 818 - 820
(2007/10/02)
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